The oysters are believed to be carrying Norovirus, which causes nausea, vomiting, diarrhea and stomach pain. The virus is highly contagious from the first moment a patient begins to feel ill, the FDA said, and spreads quickly. It is especially likely to spread in nursing homes and day care centers, the agency said.

The contaminated oyster meat was sold in three-pound bags. The oysters were already shucked, meaning that they had been removed from their shells. The labels on the packages indicated that they should be used by February 2013.

Anyone who purchased these oysters should throw them away — either in the trash or in the garbage disposal, the FDA said. If you've already eaten them and have not become ill, don't worry about it. But if you do become ill after eating them, consult a doctor, and be aware that the virus is contagious.

Consumers with questions about the recalled oysters should call Korean Farms Inc. at (562) 789-9988. The federal government also has a hotline to answer questions about seafood safety. The hotline can be reached at (888) SAFEFOOD.